There are some decent ideas here that would go much further with better feedback. If the sword projectile becomes a random chance when not at full health it could be visualized in some way to show that the next attack the player does will have the projectile, either a diceroll, roulette, or other gambling icon could flavor this.
Enemies take a bit too long to kill, I expected the sword projectile to do more damage to them as a reward for staying healthy but it felt the same. The knockback is a good idea but would do better with more pronounced, brighter hit flash on the enemy than just the quick flash of red. Hitpause for the game time and hitstun for the enemy to be unable to act for a bit after being attacked would also be nice.
Some way to mark where to go or where I've been would go a long way to encourage exploring whether that be a map or a hallway of corpses or something else. Not a fan of the enemies just respawning a few seconds after I kill them, makes me want to just avoid them unless I need health.
There were also a few times where a dead enemy wouldn't disappear and would just block my path as a red sprite of damage until they respawned.
I appreciate the arcade aesthetic a ton though.